The present invention relates to a power converter device.
Conventionally, when stopping rotation of a permanent magnet synchronous motor, it is common to stop power supply thereto, simply, and thereby stopping it naturally, with using an axial load and air resistance thereof.
When there is necessity of stopping the permanent magnet synchronous motor, abruptly, it is decelerated for a predetermined time or down to a predetermined ration speed, through regenerative braking, and thereafter it is stopped naturally.
Or, there is already known a method, so-called a direction current braking (or DC braking) of turning ON, either one (1) phase or two (2) phases on a positive (+) electrode side (s) of a switching circuit, with a negative side of other phase, continuously, so as to run direct current through that motor, thereby achieving the braking thereof.
As is disclosed in the following Patent Document 1, there is also already known a method of turning ON either one (1) phase on the negative electrode side of the switching circuit, while brining the positive electrode side of the remaining other phases into a PWM operation; thereby conducting the DC braking.
However, when decelerating or stopping the permanent magnet synchronous motor through the DC braking, excessive current is generated when it is rotating at high speed, and this results into demagnetization and burning of that motor, or breakage of a switching element(s) of a power converter device. Also, if the power converter is provided with a protection with using an over-current, an output is cut off because of that protection, and the permanent magnet synchronous motor is brought into a free-run condition; therefore, it is impossible to execute the DC braking with stability.
In the following Patent Document 1 is disclosed a method of decelerating the motor through reversed phase braking, when it is rotating at the high speed, so as to detect that the rotation speed reaches to a certain speed of a low rotation speed, and thereby switching it into the DC braking.